Many homes and buildings commonly use electric gates to protect their passageways, providing both convenience and security for the occupants. The typical electric gate blocks entrance to the structure, effectively preventing unwanted intruders from gaining access. When a proper user wants access, the gate control system is energized by the operator to temporarily open the gate.
The typical electric gate system uses a central control circuit to regulate operation of the gate. Electric gates are often controlled remotely, such as by a remote transmitter kept in a car, or alternatively can be opened by the use of a key switch. Once energized, the gate either slides out of the blocking position, or pivots upward, to a fully open position allowing cars or pedestrians to enter or exit the passageway. While the simpler systems use timing circuits which keep the gate open for a fixed period of time to allow the car to enter or exit, more sophisticated gate controllers often utilize circuitry linked to sensors which detect the presence of the moving cars. In each of these systems, the gate automatically closes once the sensor is tripped or the specified time elapsed.
A problem frequently experienced with such systems is that the gate remains in an open state too long. The typical gate is large in comparison to an automobile. It is common for entering cars to have entered past the gate long before the gate has reached the fully open position. The gate would then remain fully open for a brief period of time, then begin the closing process. While this period of time is slight, it could be enough to allow a second car or other pedestrian intruder to enter, thus compromising the security system.
Electric gate systems which close the gate immediately after a car has entered are known in the industry One such system is disclosed in U.S. Pat. No. 2,801,844, for "Automatic Door Control" issued to Cook. The Cook patent uses a photo-electric means comprising a light source and photo-electric relay to sense the passage of an automobile and command the closing of the gate. However, a drawback of the Cook door closing system is that photo-electric relays and light sources are very unreliable, due to the susceptibility of the photo-electric relay to obscuration by dirt or dust. For this reason, most modern electric gates use a wire loop sensing system, rather than a photo-electric system.
In a wire loop system, a wire is embedded in the driveway forming a large loop adjacent to the gate passageway. An electric current is conducted through the loop which acts as an inductor. When an automobile approaches the gate, the driver initiates the gate opening by use of either a key switch or an RF transmitter. As the vehicle passes over the driveway portion containing the loop, the metal and mass of the vehicle changes the inductance of the loop, altering the current output. The control circuit for the electric gate senses the change in current and keeps the gate open during this period of time. After the car has passed, and the current in the loop has returned to a normal level, the control circuit initiates the gate closing. Nevertheless, if the vehicle has entered the passageway before the gate has fully opened, the control system will still bring the gate to the fully open position before beginning the closing cycle. Therefore, even wire loop sensing systems have the same problem of the gate remaining open too long, allowing unwanted intruders to follow a vehicle through the passageway before the gate closes.
Therefore, it would be advantageous to provide a system for use within a wire loop sensing system which would close the electric gate immediately after a vehicle has passed the loop rather than delaying until the gate reaches the fully open position. Further, it would also be desirable to provide a system which could be easily added by modifying a pre-existing control circuit and wire loop sensing system, rather than by replacing the control circuit.